OBJECTIVE  To reduce starch leaching and delay the starch pasting process by optimizing the extraction temperature of Dioscoreae Rhizoma pieces and to investigate the role of excipient(low-molecular-weight sugar) addition in improving the solubility of Dioscoreae Rhizoma extract and its formula granules.

METHODS  Differential scanning calorimetry(DSC) was used to determine the temperature range of Dioscoreae Rhizoma starch gelatinization and to analyze the effects of different added amounts of small molecular sugars(lactose and glucose) on the gelatinization properties of Dioscoreae Rhizoma starch. Based on the gelatinization temperature of Dioscoreae Rhizoma starch, the extraction temperature of Dioscoreae Rhizoma pieces was optimized, five methods of reflux extraction(conventional extraction method), 100 ℃ water bath extraction, 90 ℃ water bath extraction, 80 ℃ water bath extraction, 70 ℃ water bath extraction were used to prepare the Dioscoreae Rhizoma extracts and analyze the solubility of each extract, meanwhile, the effects of five extraction methods with different temperatures on the characteristic fingerprint, extract yield, contents and transfer rates of allantoin and adenosine, as well as contents of polysaccharides and starch of Dioscoreae Rhizoma extract were investigated. In addition, based on the DSC screening results, 20% lactose was added during the extraction or concentration process at 90, 80, and 70 ℃ to verify the effects of lactose on solubility and transfer rate of active ingredients.

RESULTS  The DSC results showed that the onset pasting temperature of Dioscoreae Rhizoma starch was (73.90±0.19)℃, and the peak pasting temperature was (82.25±0.23)℃. The addition of different contents of lactose and glucose could improve the pasting temperature of Dioscoreae Rhizoma starch, and lactose(20%) had the most obvious effect. The solubility of the Dioscoreae Rhizoma extracts prepared by the four water bath extractions showed an increasing trend with the decrease of temperature, and compared with the reflux extraction and 100 ℃ water bath extraction, 90, 80, and 70 ℃ water bath extractions were able to improve the solubility of the Dioscoreae Rhizoma extracts significantly. The HPLC characteristic chromatograms of the Dioscoreae Rhizoma extracts prepared by the five extraction methods showed no obvious differences, indicating that their quality was stable. Compared with the reflux extraction and 100 ℃ water bath extraction, the Dioscoreae Rhizoma extract prepared by water-bath extraction at 80 ℃ had the highest allantoin and adenosine contents and their transfer rates, followed by 90 ℃. The polysaccharide and starch contents of the Dioscoreae Rhizoma extracts prepared by the four water bath extraction methods showed a decreasing tendency with decreasing temperatures, and among them, the polysaccharide contents of Dioscoreae Rhizoma extracts were significantly reduced by the 80 and 70 ℃ water bath extraction. The results of lactose addition validation experiments showed that the addition of 20% lactose at the extraction or concentration stage had no significant effect on the allantoin and adenosine transfer rates and significantly improved the solubility of the extracts at 90, 80 and 70 ℃.

CONCLUSION  Using 80–90 ℃ water bath extraction method to prepare Dioscoreae Rhizoma extracts, and adding lactose(20%) in the extraction or concentration stage can significantly improve its solubility while guaranteeing the dissolution of active ingredients, providing data support for the improvement of the extraction process of Dioscoreae Rhizoma, and theoretical basis for the improvement of the solubility of the Dioscoreae Rhizoma formula granules.